Lexington Weather

Lexington, Massachusetts, USA

69°F
8/17/2022 7:33pm 
  • Lexington Conditions: Overcast
  • Temperature: 69.4°F / 20.8°CColder 0.4°F than last hour.
  • Dew Point: 57.2°FDecreased 1.6°Fsince last hour.
  • Relative Humidity: 65%Decreased 3.0% since last hour.
  • Wind: Calm, 10-min avg: Calm, gust: None
  • Barometer: 29.84 inFalling 0.02  inHg/hr Falling Slowly
  • Visibility: 10 miles
  • Rain Today: 0.00 in
  •   

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 141412
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1012 AM EDT Sun Aug 14 2022

.SYNOPSIS...
Another spectacular late summer day is in store today with
plentiful sunshine and comfortable humidity. High pressure moves
offshore on Monday with cool onshore flow developing but mostly
dry weather should prevail. A coastal low pressure could bring 
periods of rain later Tuesday into Thursday but this is not set 
in stone and will depend on the track of the storm system. While
cooler than normal temperatures are favored for most of the 
week, temperatures and humidity levels rise Friday into the 
weekend with limited chances for pop-up showers or storms.

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...

1015 AM Update: 

A gorgeous morning in progress with abundant sunshine, temps
rising thru the 70s and comfortable dew pts in the 50s. All of
this captured nicely in our previous forecast. Only wrinkle in
the forecast (albeit minor), is the cyclonic swirl over NJ,
which shows up as a mid/upper level short wave trough and a cold
pocket of -15C air at 500 mb. This is a shallow trough and will
be running into a very dry airmass over SNE, with PWATs less 
than 1 inch. Hence, no impact other than mid/high cloudiness 
overspreading CT/RI and southeast MA (especially the south 
coast) this afternoon. Thus, sunshine being partially obscured 
this afternoon.

Otherwise, warm this afternoon with highs 80-85, upper 70s high
terrain and at the coastline due to afternoon seabreezes. 
Remaining comfortable with dew pts staying in the 50s along 
with light winds. Enjoy! 

&&

.SHORT TERM /8 PM THIS EVENING THROUGH 6 PM MONDAY/...

Tonight...

It will not be nearly as cool as the previous night due to more 
widespread cloud cover but with dew points in the 50s, overnight 
lows will be fairly comfortable ranging from the upper 50s to mid 
60s. 

Monday...

A highly anomalous H5 trough will dig even deeper into the Mid 
Atlantic states per the EC and GFS ensemble guidance. With anomalous 
ridging developing east of Newfoundland and Labrador, this will help 
induce a surface pressure gradient from northeast to southwest. Long 
story short, easterly to northeasterly onshore flow will be the main 
story for Monday. High pressure moves offshore during the day, 
allowing for a distant low pressure system to begin its voyage up 
the Atlantic seaboard. More details in the long term section 
regarding its potential evolution over the course of the work week. 
More clouds than sun but remaining mostly dry, although a few 
showers could not be ruled out, especially across the Worcester 
Hills and East slopes due to upslope effect. East winds will keep 
eastern MA coast cooler than further inland. Still quite pleasant 
with temps just below to near normal. Highs upper 70s to mid 80s.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...

Highlights: 

* Monitoring track of a coastal low Tues - Thurs that could bring 
  clouds and wet weather Wed-Thu, but this is not set in stone with 
  considerable uncertainty on the track. Temps cooler than normal 
  Tue-Thurs.

* Turns warmer and more humid late week into the weekend, with 
  limited chances for pop-up showers/t-storms.

Details:

Monday Night through Thursday Night:

Speaking broadly, the large-scale picture remains little changed 
from prior forecasts, with an anomalous upper trough/closed low over 
or just west of SNE. Shortwave energy rounding the longwave trough 
into the coastal mid-Atlantic looks to induce weak cyclogenesis over 
or in the vicinity of 40N/70W around Tues, with this low moving over 
or offshore of SNE in the Wed to early Thurs timeframe. Notice there 
are a lot of "or" qualifiers in that last sentence; given a rather 
complex mid-level pattern, unfortunately significant detail 
differences exist which result in outcomes ranging from a coastal 
low passing close to SNE bringing breezy onshore winds and welcomed 
significant rains to the area, or passing far enough offshore to 
maintain dry weather. Obviously quite a difference in outcomes and 
noted substantial run-to-run variation noted in the deterministic 
solutions. While the 12z GFS was a strong and western outlier, the 
00z/14th GFS came in weaker and course-corrected east a bit closer 
to Nantucket and the eastern MA coast; the 12Z/13th ECMWF on the 
other hand was fairly close to the 12z/13th GFS, but it's 00z/14th 
solution also adjusted eastward by a significant margin, leading to 
dry weather with a coastal low impacting Nova Scotia. The 00z/14th 
Canadian GEM is something of a middle road between the GFS and the 
ECMWF.

GEFS/EPS ensemble member lows show considerable longitudinal 
spread/lack of clustering as the cyclone nears our southern waters; 
with member lows painted from just south of Long Island to the 
waters south of Nova Scotia. The ensemble mean low track have shown 
an eastward tendency. Thus, overall a lower-confidence outlook, but 
there is some indication that early morning Wed to early Thurs looks 
to feature decent probabilities for wet weather for RI and eastern 
MA, and less of a chance further in the interior.

Will continue to take an ensemble-mean approach for the forecast. 
Anticipate mainly dry weather Tues, with an increasing trend in rain 
chances after midnight and especially Wed to around 35-50%, highest 
near the eastern coast and less further in the interior. Cyclone 
should pull away into Thurs with PoP going to sub-mentionable levels 
from S to N. EPS/GEFS ensemble QPF probs in a 24 hr period between 
12z Wed to 12z Thurs are fairly solid (50-70%) for 0.1 inches or 
greater rains, lower for 0.5 inches or greater (20-40%) rains, and 
are very low to nil (0-20%) for 1 inch or greater rains. 

Probably will have an enhancement to NE winds, especially Wed. 
Depending on the location/strength of the cyclone and how slow it 
moves poleward, could have some splashover or very minor coastal 
flooding along the eastern MA coast given NE/ENE winds over several 
tide cycles and a building fetch raising offshore seas. A solution 
like the 00z GFS and/or the prior 12z ECMWF would favor this. 
However at 10-10.5 ft astro tides would need a 2 to 2.5 ft surge to 
start causing issues; thus is viewed as a low prob outcome and will 
hinge greatly on the above factors which are in no way set in stone. 

Friday through Sunday Night:

Bermuda ridge over the west-central Atlc retrogrades toward the west 
with increasing SW flow and rising 500 mb heights. Looks to be a 
generally dry weather pattern, aside from diurnal shower/t-storm 
chances. May be some better chance/more storm covg later in the 
weekend or Monday but unclear which day or days may be more favored. 
Temperatures and humidity levels trend back to those more typical of 
summer, highs into the mid to upper 80s interior and coastal 
plain/70s-low 80s coast with mid-60s dewpoints returning.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels:

Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent.

14z TAF Update: no changes, VFR cloud bases, dry runways and
light winds, locally onshore for coastal terminals. Earlier
discussion below.

==================================================================

Today: High confidence.

Mostly VFR. Winds switching from W/NW to E/SE by the afternoon 
hours. 

Tonight...High confidence. 

Mostly VFR. N winds across interior terminals but SE winds for Cape 
terminals. Winds 5 to 10 kt. 

Monday...High confidence. 

Mostly VFR. E winds at 5 to 10 kt. 

KBOS...High confidence. 

KBDL...High confidence.

Outlook /Monday Night through Thursday/...

Monday Night: VFR. 

Tuesday: VFR. Breezy. Slight chance RA.

Tuesday Night: Mainly VFR, with local MVFR possible. Windy with
local gusts up to 30 kt. Slight chance RA.

Wednesday: Mainly VFR, with areas MVFR possible. Windy with
local gusts up to 30 kt. Chance RA.

Wednesday Night: Mainly VFR, with areas MVFR possible. Breezy.
Chance RA.

Thursday: VFR. Breezy. Slight chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

Low - less than 30 percent. 
Medium - 30 to 60 percent. 
High - greater than 60 percent.

1015 AM Update...spectacular boating weather today, with light
winds, dry weather, good vsby and tranquil seas. Enjoy! Earlier
discussion below.

================================================================

Through Monday...High confidence.

Seas and winds will remain below SCA thresholds for the forecast 
period. S winds today will turn E on Monday. Seas 1-3 ft. 

Outlook /Monday Night through Thursday/... 

Monday Night: Winds less than 25 kt. 

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Slight chance of rain. 

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Seas up to 5 ft. Chance of rain. 

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 9 ft. Rain likely. 

Wednesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain. 

Thursday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Loconto/Chai
NEAR TERM...Nocera/Loconto/Chai
SHORT TERM...Chai
LONG TERM...Loconto
AVIATION...Nocera/Loconto/Chai
MARINE...Nocera/Loconto/Chai
      

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